These studies are designed to advance our understanding of impulsive behavior and its relation to drug abuse by, i.) developing valid animal models of impulsive behavior and operationalizing different concepts of impulsivity, ii.) studying how both acute and chronic exposure to the drug of abuse methamphetamine (METH) affects impulsive behavior, iii.) studying the roles the neurotransmitter systems dopamine (DA) and serotonin (5HT) in impulsive behavior, and iv.) studying the roles of 5HT and DA in mediating the effects of METH on impulsive behavior. Impulsivity is a complex concept that refers to a range of different behaviors, and has been modeled in several laboratory procedures. However, few studies have assessed the relationships among the different measures. We will investigate 5 behavioral procedures that are thought to model important aspects of impulsive behavior in rats. Two of the tasks measure discounting, or preference for immediate vs delayed or certain vs uncertain positive consequences. A third task measures the animals' ability to wait for a delayed large reward when a small reward is available immediately. A fourth task measures "risk taking" by measuring preference for a safe small rewards vs risky large rewards which are sometimes followed by punishment. The final procedure measures the ability of the rat to stop (inhibit) an ongoing prepotent response. We plan to study the effects of both acute and chronic exposure to methamphetamine. We plan to investigate the role of serotonin and dopamine on impulsivity and on the effects of methamphetamine. This project is being conducted in parallel to a separate project using humans. The results of the rat and human studies will be compared to examine concordance between species in the behavioral processes, and to assess the validity of the rat models to human behavior. In sum, the proposed studies will advance our understanding of the behavioral and neural processes mediating impulsive behaviors, and of the effect of drugs of abuse on these behaviors.